DESCRIPTION: Utilizing LPS as an immune stimulus for activating the acute phase response, detailed neuroanatomical, immunocytochemical, tract tracing, and in situ hybridization techniques are proposed to test a novel model of the central organization of the febrile response to endotoxin. Based upon a substantial amount of preliminary data, prostaglandins induced by LPS are proposed to activate GABA neurons in the VMPO. These inhibitory neurons in the VMPO are proposed to activate GABA neurons in the BNST and PFA which, in turn, exert tonic inhibitory control over the PVN. Thus, by means of a dual inhibitory circuit involving the BNST and PFA, activation of the VMPO leads to activation of the PVN, which in turn activates autonomic and endocrine pathways that produce the febrile response. First, by utilizing selective doses of IV LPS and multiple labelling techniques, the applicant proposes to combine the immunocytochemical localization of c-fos protein with anterograde and retrograde neuroanatomical tract tracing techniques and GABA, galanin, TH, enkephalin, and cyclooxygenase-2 immunocytochemistry or in situ hybridization procedures. These studies will establish the chemical specificity and connectivity of the proposed dual-inhibitory model of the acute phase response to LPS. In additional studies, the febrile response will be measured following highly localized injections of GABA agonist/antagonist into the BNST and PFA in combination with c-fos immunocytochemistry as well as determine whether the injection of GABA antagonist into the BNST and PFA block the febrile response to LPS.